Electric switch

ABSTRACT

The present invention relates to an electric switch including a hollow cylindrical casing delimiting a cavity, and an actuator that can slide inside the cavity along an axial direction defined by the casing, and including at least one upper part positioned at least partially outside the casing and at least one lower part positioned inside the cavity. The electric switch also includes a contact block movable under the action of the actuator along the axial direction between two specific positions, namely upstream and downstream contact positions, with the contact block having at least two conductive areas, namely upstream and downstream conductive areas respectively positioned at the two ends of an oblong opening formed inside the contact block, and with the ends positioned in an offset manner along the axial direction. The electric switch further includes a pair of electrical contacts, namely upstream and downstream electrical contacts respectively projecting into the oblong opening. The upstream or downstream conductive area, respectively, and the upstream or downstream electrical contact, respectively, are electrically connected in the upstream or downstream contact position, respectively, of the contact block, thus closing a first electrical circuit or a second electrical circuit, respectively.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to European Patent Application No.15193656.4 filed Nov. 9, 2015, the contents of which are incorporatedherein by reference in their entirety.

TECHNICAL FIELD

The present invention relates to an electric switch comprising anactuator that is axially movable inside the housing of the switch.

PRIOR ART

At present there is a relatively wide range of sensors that can be usedin automated process control installations. One possible sensor is anelectric switch operable by a push button and positioned so as to detecta limit state of a given device. One application that may be envisagedmay, for example, be the detection of the opening and closing of anelectromagnetic brake. This is provided by placing an electric switch insuch a way that it is actuated in the middle of the air gap of theelectromagnetic brake. When the brake is closed, the air gap is alsoclosed, thus actuating the switch. When the brake is opened, the switchis actuated when the opening of the air gap is beyond the release pointof the switch. The electric switches used in this type of applicationusually operate on the principle of snap-action closing, in which thepush button, by pressing on a spring, changes the position of a movingelectrical contact. However, these snap-action switches arecharacterized by a differential movement of the spring, creating ahysteresis phenomenon. This is because, when the device returns to itsoriginal state, the push button of the snap-action switch releases itspressure on the spring, thereby changing the position of the movingelectrical contact. Owing to the differential movement of the spring inthis release phase, however, the closing or opening of the first andsecond electrical circuits does not take place for the same limit statesas it does in the compression phase of the spring. This results in alack of reliability in this type of electric switch, which cannotprovide precise detection of the variation of a small air gap.

Additionally, brake manufacturers find it useful to monitor the wear ofthe brake, which is manifested by an increase of the air gap. Thismonitoring requires the use of a second snap-action switch.

The object of the present invention is therefore to provide an electricswitch that is free of the drawbacks of snap-action electric switchesand enables both the air gap opening and the brake wear to be monitoredsimultaneously.

DISCLOSURE OF THE INVENTION

To this end, according to the invention, an electric switch is proposed,comprising:

-   -   a hollow cylindrical casing delimiting a cavity,    -   an actuator that can slide inside said cavity along an axial        direction defined by the casing, said actuator comprising at        least one upper part positioned at least partially outside the        casing and at least one lower part positioned inside said        cavity,    -   a contact block which is movable under the action of said        actuator along said axial direction between two specific        positions, namely an upstream contact position and a downstream        contact position, with an oblong opening formed inside said        contact block, said contact block having at least two conductive        areas, namely an upstream conductive area and a downstream        conductive area, respectively positioned at the two ends of said        oblong opening, said ends being positioned in an offset manner        along said axial direction,    -   a pair of electrical contacts, namely an upstream electrical        contact and a downstream electrical contact respectively,        projecting into said oblong opening,

wherein said upstream or downstream conductive area, respectively, andsaid upstream or downstream electrical contact, respectively, areelectrically connected in the upstream or downstream contact position,respectively, of said contact block, thus closing a first electricalcircuit or a second electrical circuit, respectively.

Other advantageous configurations of the present invention are definedin the dependent claims 2 to 15.

In this configuration, the electric switch of the present invention hasnumerous advantages over snap-action electric switches. In the firstplace, it is easy to manufacture, owing to its lack of structuralcomplexity. This results in a low production cost. Secondly, by contrastwith snap-action switches, it does not give rise to the aforementionedhysteresis phenomenon. Precise detection is therefore possible, becauseof the absence of this phenomenon of hysteresis. Thirdly, the opening orclosing of the electrical circuits always takes place for the samelevels of external thrust exerted on the actuator. In the fourth place,it can easily be adapted to users' requirements because of the use of asingle contact block linking the pair of moving electrical contacts.Thus, by modifying the spacing between these moving electrical contacts,that is to say the axial width of the oblong opening formed inside saidcontact block, it is possible to modify the travel for moving from theopen position of the first electrical circuit to the closed position.

BRIEF DESCRIPTION OF THE DRAWINGS

Other characteristics and advantages of the present invention will bemore clearly understood from a perusal of a particular embodiment of theinvention, and by reference to the drawings, in which:

FIG. 1 is a partially cut-away perspective view of a switch according tothe invention;

FIG. 2 is an axial sectional view of the switch shown in FIG. 1, in afirst position of use of the switch, the first electrical circuit beingopen and the second electrical circuit being closed;

FIG. 3 is a view similar to FIG. 2, but in a second position of use ofthe switch, the first electrical circuit being closed and the secondelectrical circuit being open;

FIG. 4 is a sectional view taken along the line A-A of FIG. 2.

DETAILED DESCRIPTION OF AN EMBODIMENT OF THE INVENTION

With reference to FIGS. 1 to 4, an electric switch according to theinvention is represented. This electric switch 10 is formed by a hollowcylindrical casing 11 open at its lower 11 i and upper 11 j ends, anddelimiting an internal cavity 12 of circular section. According to otherexemplary embodiments, the cavity 12 may, evidently, have a crosssection which is rectangular or any other suitable shape.

In the present description, unless specified otherwise, an axialdirection is a direction parallel to the main axis X of the cavity.Additionally, a radial direction is a direction perpendicular to themain axis X of the cavity and intersecting this axis. Unless specifiedotherwise, the adjectives and adverbs “axial”, “radial”, “axially” and“radially” are used with reference to the aforesaid axial and radialdirections. Similarly, an axial plane is a plane containing the mainaxis X of the cavity, and a radial plane is a plane perpendicular tothis axis. Additionally, an axial section is a section along an axialplane, and a radial section is a section along a radial plane.

Furthermore, unless specified otherwise, the adjectives “upper” and“lower” are used with reference to the direction of the axis X as shownon FIGS. 2 and 3. Thus the axis X runs from the upper end of the casingtowards its lower end.

Finally, the terms “upstream” and “downstream” are defined with respectto the direction of the axis X, which corresponds to the direction ofmovement, inside the cavity, of the actuator which is defined in thefollowing text of this description.

The outer periphery of the casing 11 is advantageously provided with athread 13 over almost the whole of its length, to facilitate itsfastening to a support structure by screwing. A plastic bush 14 ofsubstantially tubular shape is inserted into the cavity 12. The bush 14defines an internal housing 15 in which an actuator 16 is slidablyreceived. As shown in FIG. 3, this internal housing 15 is delimited, onthe one hand, by an upper annular shoulder 18 which limits the movementof the actuator 16 in the upstream direction, and, on the other hand, bya cap 19 fastened at the lower end of the bush 14, said cap 19 limitingthe movement of the actuator 16 in the downstream direction. As shown inFIG. 2, the actuator 16 takes the form of two parts, namely an upperpart 16 j which projects from the casing 11 at its upper end 11 j, and alower part 16 i, which slides inside the internal housing 15 of the bush14. The upper part 16 j of the actuator 16 is completely covered by anelastic membrane 17 whose edges are clamped between the upper end 11 jof the casing 11 and the upper annular shoulder 18 of the bush 14, saidmembrane 17 thus preventing any infiltration of dust or liquid into thecasing 11.

The actuator 16 is configured to change the operating state of theswitch 10 according to the axial thrust exerted on the upper part 16 jof said actuator. In fact, depending on the intensity of this axialthrust, the actuator 16 may move in a downstream or upstream direction,thus causing the opening or closing of electrical circuits. Theseelectrical circuits are, notably, formed by fixed electrical contactsand moving electrical contacts designed to come into contact with saidfixed electrical contacts when the actuator 16 is in what is called theopen position, and to cease being in contact with said fixed electricalcontacts when the actuator is in what is called the closed position.

In the variant embodiment shown in FIGS. 1 to 4, the electric switch 10comprises two fixed electrical contacts, namely an upstream fixedelectrical contact 21 and a downstream fixed electrical contact 22,which are positioned in an offset manner along the axial directioninside the housing 11. Advantageously, these fixed electrical contacts21, 22 are fitted in the thickness of the bush 14, each taking the formof an L-shaped metal rod, of which one segment 21 r or 22 r extendsradially while the other segment 21 a or 22 a extends axially. For thispurpose, the bush 14 comprises a plurality of radial channels 23 r andaxial channels 23 a, formed in its thickness, said channels beingdesigned to house at least partially said radial segments 21 r, 22 r andaxial segments 21 a, 22 a of the electrical contacts 21, 22. The radialsegments 21 r, 22 r of the electrical contacts 21, 22 project into acentral void 24 of the actuator 16 in two axially offset positions, theradial segment 21 r of the upstream fixed electrical contact 21 beingpositioned upstream from the radial segment 22 r of the downstream fixedelectrical contact 22.

The electric switch 10 also comprises two moving electrical contacts,namely an upstream moving electrical contact and a downstream movingelectrical contact, which are positioned in an offset manner along theaxial direction inside the housing 11. In the illustrated variant, thedownstream and upstream moving electrical contacts are combined within asingle contact block 25 housed slidably inside the central void 24 ofthe actuator 16, and take the form, respectively, of upstream 25 j anddownstream 25 i conductive areas positioned at the axial ends of anoblong opening 26 formed inside said contact block 25. The contact block25 is positioned in such a way that the radial segments 21 r, 22 r ofthe electrical contacts 21, 22 project into said oblong opening 26, theupstream conductive area 25 j being positioned upstream of the radialsegment 21 r and the downstream conductive area 25 i being positioneddownstream of the radial segment 22 r. Advantageously, the contact block25 is entirely made of a conductive material. In the illustratedvariant, the contact block 25 takes the form of a parallelepipedal blockhaving two opposite lateral faces 25 a, 25 b which are perpendicular tothe radial segments 21 r, 22 r of the fixed electrical contacts 21, 22.The oblong opening 26 passes through each of said lateral faces 25 a, 25b so that each of the fixed electrical contacts 21, 22 can project intothe oblong opening 26 from a different lateral face. The contact block25 slides inside the central void 24 under the combined action of anupstream spring 27 and a downstream spring 28. The upstream spring 27bears at its lower end on the upper face of the contact block 25 and atits upper end on an upper stop element 29 j fixed to the actuator 16. Inthe illustrated variant, this upper stop element 29 j is formed by theend of the central void 24. In this configuration, the external axialthrust exerted on the actuator 16 tends to move the contact block 25 viathe upstream spring 27 towards an upstream contact position, in whichthe upstream conductive area 25 j is in contact with the upstream fixedelectrical contact 21. If the external axial thrust on the actuator 16from this upstream contact position is increased, the contact block 25will remain immobile on the fixed contact 21 under the action of thespring 27, while the actuator 16 will undergo an additional travel. Thedownstream spring 28 bears at its upper end on the lower face of thecontact block 25 and at its lower end on a lower stop element 29 i fixedto the bush 14, and therefore to the casing 11. In the illustratedvariant, this lower stop element 29 i is formed by an inner face of thecap 19, which is centrally recessed to receive said lower end. In thisconfiguration, the downstream spring 28 exerts an axial thrust on theassembly formed by the actuator 16 and the contact block 25, in such away that it tends to move this assembly towards a downstream contactposition, in which the downstream conductive area 25 i is in contactwith the downstream fixed electrical contact 22. Advantageously, thisassembly is entirely made of conductive metal. In the illustratedvariant, the stiffnesses of the upstream and downstream springs 27, 28are selected so that the contact block 25 is in its downstream contactposition when the actuator 16 is not subjected to any external axialthrust, as shown in FIG. 2. On the other hand, the stiffness of theupstream spring 27 is advantageously greater than the stiffness of thedownstream spring 28, in such a way that, during the movement from thedownstream contact position to the upstream contact position, theupstream spring 27 does not undergo previous compression before thecontact block 25 starts to move. This is because such previouscompression could retard the opening of the electrical circuit of whichthe downstream electrical contact 22 forms part, thereby preventing theimmediate detection of an external axial thrust exerted on the actuator.The stiffnesses of the upstream and downstream springs 27, 28 are alsoadvantageously selected so that the compression of the upstream spring27 begins when the contact block 25 is in its upstream contact position,as shown in FIG. 3, and when the actuator 16 is subjected to anadditional external axial thrust. Thus an additional movement of theactuator 16 in the downstream direction from the position shown in FIG.3 will not cause an additional movement of the contact block 25 in thedownstream direction, but simply a compression of the upstream spring27, thus preventing any damage to the upstream fixed electrical contact21.

The variant embodiment shown in FIGS. 1 to 4 is evidently not limitingon the invention. It is only one of the possible embodiments of theinvention. However, it differs from the other possible embodiments inthe choice of using two completely distinct sub-assemblies, namely afirst sub-assembly formed by the casing alone and a second sub-assemblyformed by the plastic bush in which the actuator, the moving contactblock, the pair of fixed electrical contacts and the upstream anddownstream spring are positioned. In this configuration, the assemblyand disassembly of the electric switch are easily carried out simply byinserting the second sub-assembly into the first sub-assembly. The usercan therefore easily modify the electric switch by changing only thesecond sub-assembly, without changing the first sub-assembly.

The invention claimed is:
 1. Electric switch comprising: a hollowcylindrical casing delimiting a longitudinal cavity extending along anaxial direction defined by the casing, an actuator that can slide insidesaid longitudinal cavity along said axial direction, said actuatorcomprising at least one upper part positioned at least partially outsidethe casing and at least one lower part positioned inside saidlongitudinal cavity, a contact block which is located inside saidlongitudinal cavity and which is movable under the action of saidactuator so as to slide inside said longitudinal cavity along said axialdirection between two axial positions inside said longitudinal cavity,said two axial positions including an upstream contact position and adownstream contact position, with an oblong opening formed inside saidcontact block, said contact block having at least two conductive areas,including an upstream conductive area and a downstream conductive area,respectively positioned at ends of said oblong opening, said ends beingpositioned in an offset manner along said axial direction, a pair ofelectrical contacts, including an upstream electrical contact and adownstream electrical contact respectively, projecting into said oblongopening, wherein said upstream or downstream conductive area,respectively, and said upstream or downstream electrical contact,respectively, are electrically connected in the upstream or downstreamcontact position, respectively, of said contact block, thus closing afirst electrical circuit or a second electrical circuit respectively. 2.Electric switch according to claim 1, wherein said actuator has acentral void inside which the contact block is slidably housed. 3.Electric switch according to claim 1, wherein the contact block isformed entirely of metal.
 4. Electric switch according to claim 3,wherein the downstream spring has a lower end that bears on a lower stopelement fixed to the casing and has an upper end that bears on a lowerface of the contact block, and wherein the downstream spring and thelower stop element are formed entirely of metal.
 5. Electric switchaccording to claim 1, wherein the contact block is in said downstreamcontact position when the actuator is not subjected to any externalaxial force.
 6. Electric switch according to claim 1, wherein each ofthe electrical contacts comprises an L-shaped metal rod having at leasta first segment extending perpendicularly to an axial direction definedby the casing and at least a second segment extending parallel to saidaxial direction.
 7. Electric switch according to claim 1, wherein anelastic membrane completely covers the upper part of the actuator, thuspreventing the infiltration of dust or liquid into the casing. 8.Electric switch according to claim 1, wherein the casing has at leastone threaded area on a periphery of the casing.
 9. Electric switchcomprising: a hollow cylindrical casing delimiting a cavity, an actuatorthat can slide inside said cavity along an axial direction defined bythe casing, said actuator comprising at least one upper part positionedat least partially outside the casing and at least one lower partpositioned inside said cavity, a contact block which is movable underthe action of said actuator along said axial direction between twospecific positions, said two specific positions including an upstreamcontact position and a downstream contact position, with an oblongopening formed inside said contact block, said contact block having atleast two conductive areas, including an upstream conductive area and adownstream conductive area, respectively positioned at ends of saidoblong opening, said ends being positioned in an offset manner alongsaid axial direction, a pair of electrical contacts, including anupstream electrical contact and a downstream electrical contactrespectively, projecting into said oblong opening, wherein said upstreamor downstream conductive area, respectively, and said upstream ordownstream electrical contact, respectively, are electrically connectedin the upstream or downstream contact position, respectively, of saidcontact block, thus closing a first electrical circuit or a secondelectrical circuit respectively; wherein said actuator has a centralvoid inside which the contact block is slidably housed; and wherein thecontact block slides inside said central void under a combined action ofan upstream spring and a downstream spring with a lower end and an upperend, said upstream spring being configured to move the contact blocktowards said upstream contact position and said downstream spring beingconfigured to move the contact block towards said downstream contactposition.
 10. Electric switch according to claim 9, wherein a stiffnessof the upstream spring is greater than a stiffness of the downstreamspring.
 11. Electric switch according to claim 9, wherein the upstreamspring has an upper end that bears on an upper stop element fixed to theactuator and has a lower end that bears on an upper face of the contactblock.
 12. Electric switch according to claim 11, wherein the upper stopelement is formed by an inner face of the actuator, which defines an endof the central void.
 13. Electric switch according to claim 9, whereinthe downstream spring has a lower end that bears on a lower stop elementfixed to the casing and has an upper end that bears on a lower face ofthe contact block.
 14. Electric switch according to claim 13, whereinthe lower stop element is formed by an inner face of a cap fastened to alower end of a plastic bush of substantially tubular shape, insertedinto the casing, said cap being centrally recessed so as to receive thelower end of the downstream spring.
 15. Electric switch comprising: ahollow cylindrical casing delimiting a cavity, an actuator that canslide inside said cavity along an axial direction defined by the casing,said actuator comprising at least one upper part positioned at leastpartially outside the casing and at least one lower part positionedinside said cavity, a contact block which is movable under the action ofsaid actuator along said axial direction between two specific positions,said two specific positions including an upstream contact position and adownstream contact position, with an oblong opening formed inside saidcontact block, said contact block having at least two conductive areas,including an upstream conductive area and a downstream conductive area,respectively positioned at ends of said oblong opening, said ends beingpositioned in an offset manner along said axial direction, a pair ofelectrical contacts, including an upstream electrical contact and adownstream electrical contact respectively, projecting into said oblongopening, wherein said upstream or downstream conductive area,respectively, and said upstream or downstream electrical contact,respectively, are electrically connected in the upstream or downstreamcontact position, respectively, of said contact block, thus closing afirst electrical circuit or a second electrical circuit respectively;wherein the contact block is formed entirely of metal; and wherein alower stop element is formed by an inner face of a cap fastened to alower end of a plastic bush of substantially tubular shape, insertedinto the casing, said cap being centrally recessed so as to receive alower end of a downstream spring, and wherein the downstream spring andthe lower stop element are formed entirely of metal.
 16. Electric switchcomprising: a hollow cylindrical casing delimiting a cavity, an actuatorthat can slide inside said cavity along an axial direction defined bythe casing, said actuator comprising at least one upper part positionedat least partially outside the casing and at least one lower partpositioned inside said cavity, a contact block which is movable underthe action of said actuator along said axial direction between twospecific positions, said two specific positions including an upstreamcontact position and a downstream contact position, with an oblongopening formed inside said contact block, said contact block having atleast two conductive areas, including an upstream conductive area and adownstream conductive area, respectively positioned at ends of saidoblong opening, said ends being positioned in an offset manner alongsaid axial direction, a pair of electrical contacts, including anupstream electrical contact and a downstream electrical contactrespectively, projecting into said oblong opening, wherein said upstreamor downstream conductive area, respectively, and said upstream ordownstream electrical contact, respectively, are electrically connectedin the upstream or downstream contact position, respectively, of saidcontact block, thus closing a first electrical circuit or a secondelectrical circuit respectively; wherein each of the electrical contactscomprises an L-shaped metal rod having at least a first segmentextending perpendicularly to an axial direction defined by the casingand at least a second segment extending parallel to said axialdirection; and wherein a lower stop element is formed by an inner faceof a cap fastened to a lower end of a plastic bush of substantiallytubular shape, inserted into the casing, said cap being centrallyrecessed so as to receive a lower end of a downstream spring, andwherein the plastic bush has one or more channels formed in a thicknessof the plastic bush, said channels being designed to house at leastpartially said first and/or second segments of said metal rods.